How do salt additives improve the permeability of the thin-film composite membrane?

Various salt additives were widely used to enhance the permeability of thin-film composite (TFC) membranes. Researchers attributed the improvement in TFC membranes to the change in the polyamide (PA) layer. However, the contribution degree of PA layer to TFC membrane permeability enhancement and the effect of salt additives on the substrate are ambiguous. In this study, the effect of salt additives on the permeation resistance of FTC membranes was analyzed. The results showed that the salt additives could reduce both the permeation resistance of the PA layer and substrate, but the effect on the substrate was more pronounced. For example, after adding NaCl, the permeation resistance of the substrate in the heat curing membrane reduced from 0.1764 to 0.0201 bar h m-1, which was much more than that in the PA layer. This study revealed a new mechanism of salt additives improving the permeability of TFC membranes and deepened the understanding of the action mechanism of salt additives.